As has been described in the aforementioned applications, a slide fastener stringer generally comprises a pair of support tapes along confronting edges of which are provided rows of coupling elements which are interdigitable upon movement of a slider along these rows. In one construction which has recently found considerable favor in the art, each row of coupling elements is constituted by a substantially helical coil of a synthetic-resin monofilament, the turns of each coil being constituted as the coupling element. One side of each turn may be deformed to provide protuberances along the axis of the coil which engage with corresponding protuberances of the other coil for interlocking of the coupling elements with one another. The turns run immediately into bights which interconnect the shanks of the successive turns. The slider can be guided along these coils which can be provided with a filler core and can be stitched between the turns to the tape.
Numerous other systems utilizing basically similar principles have been proposed. For example, the turns can be fitted through openings in a knit or woven tape so that the textile threads of the tape are interposed between the turns. The coils can be replaced by so-called meanders which have an undulating configuration and can be anchored to the tape by any of the techniques described above.
A common disadvantage of all such systems is, of course, the fact that the pitch or turn spacing of the slide fastener row tends to vary with various effects adapted to modify the support tape or the threads connecting the coils to the support tape. For example, shrinkage by heat or moisture during washing of the garment, chemical action during dry-cleaning, environmental attack and the like, all are capable of modifying the parameters of the textile threads disposed between the turns of the coupling rows and hence varying the pitch of the heads.
The above-described applications, of which the present case is in part a collateral advance, recognize that some of these problems, if not all of them, can be eliminated by forming the coupling elements as part of tape-like support structures or units from which the coupling heads project along one lateral edge while the shanks are extended into pockets formed by longitudinal threads to form part of the weft or the exclusive weft for a multiplicity of such longitudinal threads. Because a shank of each coupling head or a pair of mutually abutting shanks of each coupling element are disposed in the successive pockets formed by the longitudinal threads, considerable stability is imparted to the structure and many of the disadvantages enumerated above are eliminated.
The invention in the present case is directed to a combination of the stringer with the slider and deals with problems which arise when the conventional coupling elements as described are used with a conventional slider. A slider generally comprises a shield-forming channel for the respective rows of coupling elements, these channels merging into a common outlet channel at one end of the slider. At the other end of the slider and centrally thereof there is provided a heart piece or divider which spreads apart the coupling elements of the two rows for the opening movement of the slider.
Thus the present disclosure deals with a slide fastener whose coupling rows are formed from synthetic-resin monofilaments with coupling elements formed with eyes having coupling heads pressed therein, eye-forming monofilament segments extending to either eye of the coupling heads, connecting shanks extending from these segments and bight portions connecting the shanks of adjoining coupling elements, the shanks forming part of a weft of a support structure from which the bights project. The slider which cooperates with the rows of coupling elements has a shield and channels in which the rows are guided with a divider or heart piece extending from one side of the slide fastener to the other.
Prior-art sliders have not been entirely successful although they have been constructed in various configurations to solve different problems. For example, many earlier stringers did not have a highly stable coil or row of coupling elements and the inerhead spacing or pitch did not remain constant for the reasons noted above and because the head spacing was effected adversely by the diverse method of attaching the stringer to the garment or other article. During the stitching process and as a consequence of the stitching process variations were discovered in the head spacing which detrimentally effected the ability to open and close the fastener by the movement of the slider therealong. These disadvantages were in addition to the shrinkage, stretching and distortion effects mentioned earlier. In fact, the changes did not take place equally in both slide-fastener halves so that is was not uncommon to find that the interhead spacing of one slide-fastener half, after some use of the garment, several washings or the like differed markedly from the interhead spacing of the other slide fastener half. In these cases the slide fastener became unusable.
Furthermore, especially where the garment or other article to which the rows of coupling elements were secured had closely confronting edges, one could not readily draw the slider between them without entraining the fabric with the slider so that difficulties were encountered during the fastening and unfastening process as well.
There are two techniques which have been used for interdigitating the rows of coupling elements known in the art. The first can be denominated as a coupling by spreading. In this technique, the two rows of coupling elements are maintained in the same plane, i.e. in the slide fastener plane, and the rows are bent to spread apart the adjoining copending elements so that the head of one coupling element can fit between the heads of the opposing pair of coupling elements by movement in the spreading plane. As a practical matter, the spreading of the adjacent coupling elements to accommodate the heads of the opposite elements must be considerable and hence the slider was required to have a relatively wide mouth and, consequently, a large opening angle. The article to which the coupling elements were secured resisted such spreading to an extent which depended upon the way in which the stringer was stitched to the article. In many cases, therefore, such sliders were impractical and considerable case had to be taken to ensure that the method of attachment would not be contrary to the requirements for the particular slider. Such strictures could not be observed in many instances because potential users often had to use different types of sewing machines and the like.
In the other type of interdigitation (press fitting), the coupling rows were not bent into a V-shaped configuration in a single plane but were superposed. In other words one of the coupling rows was brought into a second plane which generally lay above the slide fastener plane, the coupling elements of this row being pressed downwardly between the coupling elements of the other row. This slider requires means or special design characteristics to prevent it from being induced to slide along and open the fastener when a transverse stress is applied.